1. Field of the Invention
The present invention relates to electromagnetic transducers including conductors disposed in predetermined patterns and more particularly to patterned conductors disposed on surfaces having significant curvatures.
2. Prior Art
For accurate transduction of electromagnetic signals, transducers must have accurately known characteristics. Accurately known characteristics can be obtained in two different ways. The first is to fabricate individual transducers in an attempt to match a predetermined configuration, but with a fabrication tolerance which requires extensive testing to determine the actual characteristics of each transducer and whether it meets the intended specifications. The second is to fabricate the transducers with tight enough tolerances that simple testing can be used to establish that each transducer matches or fails to match the specifications for a standard transducer of the same design whose characteristics are accurately known from extensive testing. In the former case, substantial testing cost is added to the fabrication cost of each transducer thereby substantially increasing its cost. In the latter case the cost of extensive testing of the standard transducer is part of the initial development cost which is spread over all production transducers. It is generally recognized that the latter technique is preferable for both interchangeability of parts between systems and for limiting manufacturing and testing costs. Unfortunately, not all electromagnetic transducers are susceptible to fabrication to the tight tolerances necessary to enable the latter technique to be utilized. One type of transducer which has not been susceptible to being fabricated in the latter way is the pickup coil of the sensors used in magnetic resonance spectroscopy.
In magnetic resonance spectroscopy a strong uniform DC magnetic bias field is applied to a sample to be analyzed. This magnetic field causes the net spin axis of the electrons of the atoms comprising the sample to align parallel to the DC magnetic bias field. The sensor or pick-up coil has two halves and is located within this strong uniform magnetic field with the sample being investigated disposed between the two halves. A perturbation current is passed through this sensor coil to create a magnetic field perpendicular to the DC magnetic bias field to cause the orbits of electrons in the sample material to realign with their spin no longer in the direction of the DC magnetic bias field, and preferably perpendicular to the DC magnetic bias field. The perturbation current is then removed from the sensor coil, which removes the perturbation magnetic field. The spins of the electrons then reorient back to parallel to the DC magnetic bias field. The electromagnetic signals generated by this reorientation of the electron spins are sensed by the pick-up coil and amplified and analyzed by the electronic portion of the magnetic resonance spectroscopy machine. The frequencies of the electromagnetic signals are determined by the elements and compounds present in the sample and thus provide information which can be processed to determine the composition of the sample.
For maximum accuracy in the spectrographic analysis of the material of the sample, the sensor coil must have an accurately known configuration and must be configured in a way which causes the perturbation current through the sensor coil to generate a magnetic field which is oriented perpendicular to the main DC magnetic bias field without any significant field component parallel to the main DC bias field. Further, the pick-up coil itself should have no net turns through the bias magnetic field in order that the current through the coil will not alter that DC magnetic bias field.
One prior art magnetic resonance spectroscopy pick up coil is a hollow glass tube about 3/8 inch in inner diameter with a wall thickness of about 1/16 inch and having a sensor coil disposed on its outer surface. The sensor coil comprises two diametrically opposed "flat" or pancake coils which conform to the exterior surfce of the tube and are connected in series. The sample to be analyzed is passed through this tube and analyzed when it is located in the tube between the two halves of the sensor coil.
The sensor coil is formed through use of photolithographic techniques to define the coil in a separate, planar, copper foil which is preferably free of all magnetic materials. The copper foil is etched to leave the coil which is then mounted on and adhered to the exterior surface of the glass tube. Mounting the coil on the tube is a labor intensive process which is subject to significant variation even with the exercise of great care by the operator. As a result, sensor coils of this type must be extensively and carefully quality control tested prior to being accepted for shipment, sale and use as a sensor coils. Both the manual fabrication process and the extensive testing it makes necessary contribute significantly to the cost of such sensor coils. Since the basic material costs are minimal, the fabrication process and testing are the primary contributors to the cost.
Improved and less expensive coil designs and fabrication techniques are desirable.
Accordingly, it is an object of the present invention to provide a method of fabricating a magnetic resonance sensor which is accurately reproducible whereby the need for extensive testing is obviated.
It is also an object of the invention is to provide a magnetic resonance sensor fabrication technique which is inexpensive in order that the cost of such sensors may be reduced.
An additional object of the invention is to provide a technique for fabricating precision conductor patterns on surfaces having significant curvature.
Another object of the invention is to provide a technique for fabricating precision patterned conductors on the surfaces of a cylindrical object.
Another object of the invention is to provide a technique for fabricating precision patterned conductors on the interior surface of a hollow tube, which may be transparent.
A further object of the invention is to provide an improved magnetic resonance sensor.
A still further object of the invention is to provide a magnetic resonance sensor having improved sensitivity and accuracy.
A still further object of the invention is to provide a magnetic resonance sensor in which the pick-up coils are immediately adjacent to the sample volume being investigated.